Scalable, Tunable Josephson Junctions and DC SQUIDs Based on CVD Graphene

Tianyi Li,John C Gallop,Edward J Romans,Ling Hao

doi:10.1109/tasc.2019.2897999

Abstract

Since the carrier density and resistivity of graphene are heavily dependent on the Fermi level, Josephson junctions with graphene as the weak link can have their I – V properties easily tuned by the gate voltage. Most of the previous work on superconductor–graphene–superconductor (SGS) junctions and superconducting quantum interference devices (SQUIDs) were based on mechanically exfoliated graphene, which is not compatible with large scale production. Here, we show that SGS junctions and dc SQUIDs can be easily fabricated from chemical vapor deposition (CVD) graphene and exhibit good electronic properties. The SGS junctions can work without any hysteresis in their electrical characteristics from 1.5 K down to a base temperature of 320 mK, and the critical current can be effectively tuned by the gate voltage by up to an order of magnitude. As a result, dc SQUIDs made up of these junctions can have their critical current tuned by both the magnetic field and the gate voltage.

Highlights

D UE to their unique non-linear inductance, Josephson junctions or dc superconducting quantum interference devices (SQUIDs) have become the building blocks and key elements of superconducting qubits, which are a promising solid-state approach to realizing quantum computing [1]–[3]
We show that SGS junctions and dc SQUIDs based on chemical-vapor-deposition (CVD) graphene exhibit ideal electronic properties with the critical current tuned by the gate voltage, and can be promising candidates for applications such as superconducting qubits
By measuring the I-V characteristics of junctions of different length and width, we have found that the critical current and the normal state conductance show a linear dependence on the junction width

Summary

INTRODUCTION

D UE to their unique non-linear inductance, Josephson junctions or dc superconducting quantum interference devices (SQUIDs) have become the building blocks and key elements of superconducting qubits, which are a promising solid-state approach to realizing quantum computing [1]–[3]. Due to limitations in fabrication techniques, it is almost impossible to make perfectly identical Josephson junctions based on conventional sandwich structures. Such a problem is normally solved by replacing a single Josephson junction with a dc SQUID and accompanying it with a nearby current-carrying control line. The critical current of the SQUID can be tuned by the local magnetic field, so that the energy-level spacing of the qubit or the resonator can be tunable. We show that SGS junctions and dc SQUIDs based on chemical-vapor-deposition (CVD) graphene exhibit ideal electronic properties with the critical current tuned by the gate voltage, and can be promising candidates for applications such as superconducting qubits

METHODS

I-V Characteristics of SGS Junctions

I-V Characteristics of DC SQUIDs

CONCLUSION